1. Field of the Invention
The present invention relates to machines for washing paper stock pulp and other free-filtering materials.
2. State of the Art
According to various processes well-known in the paper making industry, paper stock pulp is formed by digesting wood chips in the presence of various chemicals in a heated pressure vessel. After discharge from the pressure vessel, the paper stock pulp must be washed and filtered to separate the wood fibers from the digestion chemicals.
One system for washing paper stock pulp is taught in U.S. Pat. No. 2,355,243. According to that patent, paper stock is diluted with water after digestion and then is picked up by a large-diameter rotating cylinder whose surface is formed of a wire mesh screen. A couch roll is positioned to press downward onto the surface of the screen-covered cylinder to express liquid from the stock and thus to form a residual blanket or mat of dewatered fibers. The system described in the patent further includes an agitation device wherein once-dewatered fibers are repulped by mixing with water. Still further, the system taught in the patent includes additional agitation devices, screen-covered cylinders, and couch rolls to wash the pulp in stages.
According to other processes well-known in the paper-making industry, materials such as waste paper and groundwood, although not digested with chemicals, must nevertheless be washed. Conventional systems for such washing are also known.